186 DISTRIBUTION. 



denticles, ivhich, according to llichter, scarcely project beyond the common canal, and have the orifice 

 situated iu the axil of the spine. 



As to the mode of life of the graptolites, he believes that by the aid of the " foot," which he 

 regards as possessing a certain amount of spontaneous mobility, they were enabled to bore into the sea- 

 bed of clay or mud, and there maintain an erect position. 



After comparing them with tlie Pennatulidce, Hi/droida, and Pobjzoa, he concludes that they are 

 most nearly related to these last, and refers to Leuckart as advocating in a letter to himself the polyzoal 

 nature of the graptolites. He adduces the rod in Bhabdop/eura as affording evidence of this view, and 

 (though the reserablauce seems to have escaped him) he might also have compared the peculiar striie 

 which he has described as usually present in the graptolites with those which exist in the adherent 

 portion of the tube in Rhabdopleura (see ' Mic. Journ.,' vol. xi, New Series, pi. viii, fig. 4), to which 

 it must be admitted they present a very striking similarity. I am unable, however, to find in Richter's 

 arguments any grounds for accepting the polyzoal affinities of graptolites, while in his comparison of 

 the two laminae of the graptolite test to the ectocyst and endocyst of a Pohjzoon it is plain that he has 

 formed an erroneous conception of the nature of the fleshy organized endocyst which constitutes the 

 essential part of the body- walls of a Pohjzoon. 



The paper concludes with au enumeration of the graptolites which occur in the Upper Silurian 

 strata (Nereitenschichten und Tentaculitenschiefern) of Thuringia, with descriptions of the new species. 

 Among the forms described as new by far the most remarkable is one which carries three vertical rows 

 of cells upon the common canal. He makes it the type of a new genus, Triplogruptvs. The propriety, 

 however, of associating this remarkable fossil with the true graptolites appears to me very doubtful. 



